Dissolved organic matter modulates the toxicity of persistent free radicals on the nematode Caenorhabditis elegans

Abstract As a type of effective soil amendment, biochars require comprehensive ecological assessment before their widespread agricultural applications, since the endogenous contaminants, especially environmentally persistent free radicals (EPFRs) in biochars certainly pose an ecological risk to soil invertebrates. In this study, Caenorhabditis elegans (C. elegans) was chosen as a model organism to assess the neurotoxicity of three rice straw biochars pyrolyzed at 500, 700, and 1000°C. After 24 h-exposure to unwashed biochars, washed biochars, and leaching liquids (supernatants), neurobehavioral parameters of L4 C. elegans larvae were determined in a liquid toxicity test. The results showed that the washed 700°C biochar particles significantly impaired the locomotion and prolonged the defecation interval at biochar concentration of 4 g·well− 1, whereas unwashed biochars and supernatants did not cause obvious impairment. At the same time, the electron paramagnetic resonance (EPR) results showed that the intensity of EPFRs in unwashed 700°C biochar was stronger than that of corresponding washed particles. It suggests that, in the liquid test, EPR signal alone does not indicate the toxicity of the particle. The accessibility and activity of EPFRs should be considered. Dissolved organic matter (DOM) has great significance in the fate, transport, and toxicity of environmental pollutants, which is beneficial for C. elegans to live longer and increase their reproductive ability. In this paper, the neurobehaviors of washed biochar were alleviated after adding supernatant back, which indicated that DOM could modulate the reactivity of EPFRs in the liquid phase.